1. Field of the Invention
The present invention relates to an optical semiconductor module for optical communication or transmission techniques. More particularly, it relates to an optical semiconductor module in which the coupling structure of an optical semiconductor element and optical transmission channel is improved, and its manufacturing method.
2. Description of the Related Art
In optical communication and transmission techniques, it is necessary to optically couple an optical semiconductor element, such as a light emission element or light reception element, to an optical transmission channel formed of, for example, an optical fiber. As one type of optical coupling, a so-called butt joint system is now being researched and developed, in which optical fibers and an optical semiconductor element are closely opposed to each other and optically coupled without a lens.
When using the butt joint system, it is important to closely locate an optical semiconductor element and optical fibers so that light does not reach an unnecessary portion of each optical fiber. Moreover, it is necessary to employ a technique for preventing the end faces of the optical fibers closely opposing the active areas of the optical semiconductor element from colliding with the active areas. Accordingly, a mechanism is required which can perform not only positioning in the direction parallel to the end face of each optical fiber, but also axial positioning.
Jpn. Pat. Appln. KOKAI Publication No. 2000-206376, for example, discloses a method for axially positioning optical fibers and an optical semiconductor element. In this method, a component is beforehand prepared by protruding optical fibers from an optical fiber holder, then accurately positioning the fibers and fixing them in position. The distance between the holder and an optical semiconductor element is controlled using a spherical spacer, thereby axially positioning the optical fibers and optical semiconductor element. Since the relative positions of the holder and optical semiconductor element are determined by the spherical spacer, and the optical fibers are protruded from the holder by a predetermined distance, an accurate fixing technique is required, which increases the manufacturing cost.
Further, Jpn. Pat. Appln. KOKAI Publication No. 2002-250846 discloses a technique for placing an optical semiconductor element on a plate with electric wiring, and positioning the optical semiconductor element and optical fibers with the plate interposed. In this technique, the distance between the optical semiconductor element and fiber end faces depends on the thicknesses of the plate, wiring and a bump needed for mounting the element, which makes it difficult to closely oppose the optical semiconductor element and fiber end faces. Furthermore, when mounting a plurality of optical semiconductor elements on the plate, it is necessary to match the configuration (heights) of the bump with all the elements. This is a very difficult technique and hence inevitably increases the mounting cost.
In addition, Jpn. Pat. Appln. KOKAI Publication No. 2001-59924 discloses a structure in which dummy bumps are located in positions on an optical semiconductor element other than the active areas of the element, the positions corresponding to the claddings of optical fibers, and the bumps are pressed against the end faces of the fibers after they are connected to wiring provide on a holding member, thereby aligning the axial positions of the optical semiconductor element and fibers. Thus, this structure uses dummy bumps. Therefore, if a plurality of optical semiconductor elements are mounted, it is necessary to adjust a large number of dummy bumps on the semiconductor elements to a certain height, or to take measures so as to prevent the bumps and/or elements from inclining when they are mounted. These things may well increase the mounting cost.
As stated above, when the butt joint system is used for optical coupling of an optical transmission channel and optical semiconductor element, it is difficult to shorten the distance between the optical semiconductor element and the opposing end face of the optical transmission channel, although it is desirable to locate them very closely. It is also difficult to reliably control the distance between a plurality of optical semiconductor elements and the optical transmission channel, or the inclination of the semiconductor elements. These things increase the mounting cost.